This may seem like a very silly question, but is it possible to create replacement parts such as barrels at higher twist rates for certain rifles? The FN FNC has not been imported to the US for over two decades if I recall, and there are scantly if any major parts available for the rifle in case anything really breaks. That leaves only two options that I can foresee, buy another rifle and cannibalize it, or make your own.

There are certain things I imagine you cannot recreate without specialty machinery or tooling, but what about parts such as the barrel that you can do on your own? This doesn't only pertain to the aforementioned rifle but for others as well. How difficult would such a thing be to do, what would it take in order to create custom replacement parts for those more uncommon firearms and so on.

Please forgive my ignorance on this topic as I'm still very new to this subject.